This invention relates to a tape guide block in a three piece type tape cassette which is composed of upper and lower cassette halves and the tape guide block, and a method of producing the same.
Three piece type tape cassettes in which a tape guide block is formed separately from upper and lower cassette halves have been proposed for the purpose of solving the problems experienced with two piece type cassettes in terms of accuracy and manufacture. Such problems still remain with three piece type cassettes, and propositions for further improvements have been made with respect to the structure of the tape guide block and the method of forming the same. However, propositions heretofore put forward have only succeeded in partially solving these problems.
For example, Japanese Patent Publication No. 50354/1981, Japanese Utility Model Laid-Open No. 87630/1978 and Japanese Utility Model Laid-Open No. 95817/1978 disclose arrangements in which mold drawing of injection molding is made in the direction of the reference level surface of a cassette half so as to set the tape guide surface of a tape guide block perpendicular to the reference level surface. Accordingly, it is necessary with such arrangements for a drawing inclination to be provided on each of the inner surfaces of upper and lower cassette halves. In Japanese Utility Model No. 95817/1978, a slanted surface is formed on a part of each of the upper and lower cassette halves on account of the need for such an inclination so that the tape guide surface is set accurately perpendicular to the reference level surface of the cassette halves. This arrangement necessitates a high degree of accuracy in manufacturing the cassette halves. On the other hand, the techniques disclosed in the other two publications do not take account of this need, and they therefore still involve the problem of difficulty in positioning the guide block accurately and stably in relation to the cassette halves.
All of the above-described techniques employ a recessed guide wall formed on the inner surface on each of upper and lower cassette halves as a basis for positioning and fixing the guide block to the cassette halves. Therefore, it is necessary for these techniques to accurately form the guide walls over a large area. The problem of the play which tends to occur between the parts also remains.
The above-mentioned Japanese Patent Publication No. 50354/1981 also discloses a measure for solving the problems of wear and heat generation caused by the friction between the guide surface and the tape. That is, guide rollers are integrally formed through the medium of tension arms constituted by thin webs so as to form a guide block on a tape guide mechanism component, and the guide rollers are resiliently shifted by virtue of the resiliency of the tension arm, thus reducing the friction and heat generation experienced. Since the integral formation of the tape guide mechanism component and the guide roller of this arrangement involves a tension arm to which a proper resiliency must be applied by the thin web, the construction of these integral parts are complicated, so that it is difficult to form these parts.
Another technique which provides a measure for solving the above-described problem of friction from a different aspect is disclosed in Japanese Patent Laid-Open No. 15879/1985. According to this technique, a guide block is formed of a non-magnetic material by die casting so as to mechanically reduce wear and heat generation caused by friction. However, this technique requires the work of finishing the shape and dimension of the guide block using tools such as bites since the guide block is formed by die casting.